To determine whether antibodies to HIV-1 (anti-HIV-1) or HTLV-I (anti-HTLV-I) were present in Zambia before (1976, 1977, 1978, 1979) and at the beginning (1981) of the recognized worldwide epidemic of these viruses. 349 serum samples, stored at -20 C, were obtained from 226 apparently healthy residents from five rural villages in Zambia (preinoculation samples in a hepatitis B vaccine trial in 1981) and from 123 patients with hepatocellular carcinoma (HCC) who were patients at a large urban university hospital (1976, 42 patients; 1977, 24 patients; 1978, 29 patients; 1979, 16 patients; 1981, 12 patients). Each sample was tested for anti-HIV-1 and anti-HTLV-I by enzyme immunoassays (EIA). Reactive samples were retested in duplicate by EIA and tested for confirmation by western immunoblot (WIB) and by radioimmunoprecipitation (RIPA) assays. None of the 226 healthy villagers or 123 HCC patients had detectable anti-HIV-1 or anti-HTLV-I. The results of these serologic tests illustrate the absence of antibodies to HIV-1 and HTLV-I in Zambia in 1976-1981, several years before the worldwide epidemic was recognized. The durability of antibodies in the sera from Zambia, which had been stored at -20 C for 9-14 years, was confirmed by testing the 123 sera from HCC patients for antibody to hepatitis B core antigen by EIA in 1990. This antibody was detected in 94 patients (76%). This study shows that in 1976-1981, HIV-1 and HTLV-I had not yet been introduced in Zambia. It is possible that these viruses could have been present in other parts of Africa prior to the worldwide epidemic; they appear not to have been prevalent in Zambia.